Although likely self-serving, it is interesting to read Nathan Leopold's own account of his motivations for the crime (though he does not discuss details of the crime itself) as well as his subsequent life in prison and his rehabilitation.
Over his 33-year imprisonment, Leopold matured from a cocky 19-year-old egoist, eager to do a "thrill" crime to prove his superiority, to a mature cocky egoist who engaged in "humanitarian" projects to prove his rehabilitation and earn his eventual parole. While traces of his egoism and sense of superiority remained--and undoubtedly his rehabilitation was methodically designed to gain his freedom after serving 33 years--it's also clear that he did dedicate the rest of his life to projects that benefitted others. These include expanding the educational facilities at Joliet and Statesville (with the assistance of Richard Loeb until Loeb's murder by another inmate in 1936) to high school and junior college level, promoting inmate enlistment for service in WWII, volunteering both as a medical technician and as a subject for research into malaria treatment and drugs (in hopes of shortening his sentence), enlisting inmates to register for cornea donations (Leopold himself donated his corneas upon his death), and studying water contamination and researching cures for leprosy in Puerto Rico after his parole there.
It's a good read and a fascinating book.